1. Field of the Invention
The invention concerns a cellular mobile telephone system usable on board a passenger transport vehicle, for example an aircraft, a train, a ship, etc.
2. Description of the Prior Art
At present it is not possible to use a portable mobile telephone terminal on an aircraft, for example, as one might in any other public place, on the one hand because it is prohibited, the radiated signal having sufficient power to interfere with onboard electronic equipment, and on the other hand because it would be necessary to place the terminal near a window in order to be able to communicate with a base station system outside the cabin of the aircraft. A telephone service is currently available in aircraft via dedicated terminals each connected by a wire to fixed equipment including an antenna outside the aircraft. The equipment constitutes an interface with a telecommunication system, for example a satellite telecommunication system. The airline company offering the service must assume responsibility for the call billing aspects.
Document WO 98/21838 describes a cellular mobile telephone system usable on board an aircraft and enabling the use of standard GSM or DCS portable terminals. According to this prior art document, each GSM or DCS portable terminal is connected to a first electro-optical converter by a short shielded wire. The converter serves a small group of nearby passengers. The first converter converts a radio frequency signal from a portable terminal into an optical signal and vice-versa.
All the first converters are connected to a central unit by a network of optical fibers. The central unit includes second converters which convert an optical signal into a radio frequency signal and vice-versa. This prior art device avoids the radio frequency radiation that could leak from a network made up of long shielded cables. The central unit is connected to a transmitter-receiver station by short shielded cables. Each station has an antenna outside the aircraft and connects the aircraft to a GSM or DCS terrestrial mobile telephone network via a network of satellites.
The central unit has functions analogous to those of a base transceiver station in a standard mobile telephone network. A standard base transceiver station is connected to a base station controller. In the prior art device described in the above prior art document, the functions of a base station controller are not provided by the central unit on board the aircraft but instead by a controller on the ground. The disadvantage of the prior art device is that it necessitates a permanent link for transmitting signaling information between the aircraft and the mobile telephone network on the ground, exactly like the link which connects a standard base transceiver station to a standard base station controller. The permanent link consumes network resources.
An object of the invention is to propose a system which is free of the drawbacks of the above prior art device and which extends the cellular mobile telephone service provided by the standard operators to passenger transport vehicles, enabling passengers to use their standard portable terminal without having to connect them to a cable and without the transportation company offering the service having to assume responsibility for the call billing aspects.